Shaft/hub connection

ABSTRACT

The shaft ( 1 ) is connected to the shaft attachment ( 2 ) by means of a thread. A bore ( 20 ) with an internal thread is incorporated in the shaft attachment and the shaft has a corresponding stem ( 10 ) which can be introduced into the threaded bore and has an external thread. An axial stop ( 11, 21 ) is arranged in each case on the shaft and on the shaft attachment. The internal and external threads have torque-transmitting flanks which are flat toward the axis and which can be connected to one another frictionally by means of radial pressure by mutual rotation of shaft and shaft attachment with interaction between the axial stops.  
     Owing to the small angle between the load-bearing flanks and the axis, the radial pressure decisive for the torque transmission is correspondingly greater than in conventional threaded connections. As a result, the axial prestressing force between the two parts to be connected can be correspondingly reduced.

TECHNICAL FIELD

[0001] The invention relates to the field of shaft/hub connections.

[0002] It relates to the connection of a shaft to a shaft attachment bymeans of a thread according to the preamble of patent claim 1. It alsorelates to a turbocharger, the turbine shaft of which is correspondinglyconnected to the compressor wheel.

PRIOR ART

[0003] Turbochargers for increasing the output of reciprocating pistonengines comprise a turbine driven by engine exhaust gases and acompressor connected to the turbine via a torque-transmitting shaft.Turbochargers for lower engine outputs advantageously have a radialcompressor of aluminum without a continuous central bore, as disclosed,for instance, by DE 44 44 082.

[0004] In this case, for production and maintenance reasons, thecompressor wheel is releasably connected to the turbine shaft.

[0005] In the known solutions, the compressor wheel is screwed onto ashaft stub with a conventional thread either directly or via anintermediate bush of steel or bronze. At least one cylindrical orconical centering seat offset relative to the thread provides for thecentering of the compressor wheel relative to the shaft.

[0006] In such a shaft/compressor-wheel connection, the compressor wheelis restrained against an axial stop on the shaft. The torquetransmission is effected frictionally in the thread via the load-bearingthread flanks pressed against one another in the axial direction. Inconventional threads, the load-bearing thread flanks are at as steep anangle to the shaft axis as possible, so that the prestressing force canact essentially normal to the surface of the load-bearing thread flanks.

[0007] The most recent increases in output of the compressors ofturbochargers necessitate an improved torque transmission from shaft tocompressor wheel. In conventional connections, this means that theprestressing force has to be increased in order to press theload-bearing flanks of the threads against one another to a greaterextent in the axial direction. However, this leads to reduced damping ofthe joint location between the parts connected to one another. Inaddition, a further restriction is the notch effect caused inconventional threads by the jump in cross section from thread turn tothread turn.

BRIEF SUMMARY OF THE INVENTION

[0008] Consequently, the object of the invention is to provide aconnection of the type mentioned at the beginning which permits animproved torque transmission with reduced axial prestress.

[0009] According to the invention, this object is achieved by thefeatures of patent claim 1.

[0010] In the connection according to the invention of a shaft to ashaft attachment by means of a thread, in which a bore with an internalthread is incorporated either in the shaft attachment or in the shaftend, and the shaft or the shaft attachment has a corresponding stemwhich can be introduced into the threaded bore and has an externalthread, and an axial stop is arranged in each case on the shaft and onthe shaft attachment, the internal and external threads havetorque-transmitting flanks which are flat toward the axis of shaft andshaft attachment and which can be connected to one another frictionallyby means of radial pressure by mutual rotation of shaft and shaftattachment with interaction between the axial stops.

[0011] Owing to the small angle between the load-bearing flanks, bearingfrictionally on one another with their large surfaces, and the axis, theradial pressure decisive for the torque transmission is correspondinglygreater than in conventional threaded connections. As a result, theaxial prestressing force between the two parts to be connected can becorrespondingly reduced.

[0012] In addition, the load-bearing flanks of flat design permitimproved centering of shaft attachment and shaft.

[0013] Further advantages follow from the dependent claims.

BRIEF DESCRIPTION OF THE DRAWINGS

[0014] An exemplary embodiment of the connection according to theinvention is shown schematically and explained in more detail below withreference to the figures. In all the figures, elements having the sameeffect are provided with the same designations. In the drawing:

[0015]FIG. 1 shows a view of a shaft with a shaft attachment having aconnection according to the invention,

[0016]FIG. 2 shows a section along the shaft axis through the connectionaccording to FIG. 1,

[0017]FIG. 3 shows an enlarged detail III-III of the connectionaccording to FIG. 2,

[0018]FIG. 4 shows a view of the shaft according to FIG. 1 in the axialdirection,

[0019]FIG. 5 shows a view of the shaft according to FIG. 1perpendicularly to the axis,

[0020]FIG. 6 shows a view of the shaft attachment according to FIG. 1 inthe axial direction, and

[0021]FIG. 7 shows a section along VII-VII through the shaft attachmentaccording to FIG. 6.

WAY OF IMPLEMENTING THE INVENTION

[0022]FIG. 1 shows a shaft 1 and a shaft attachment 2 connectedaccording to the invention to the shaft. By way of example, the shaftattachment is depicted as a cylindrical counterpart correspondingapproximately to the shaft in shape and size. As a rule, the shaftattachment is a wheel-shaped part, such as, for instance, the compressorwheel of a turbocharger.

[0023] The shaft has an external thread in the region of the connectingpoint. In the embodiment shown, the external thread is formed on theshaft end in the form of a threaded stem 10. A corresponding bore 20which is provided with an internal thread is incorporated in the shaftattachment.

[0024] For the axial positioning of the shaft attachment relative to theshaft, the shaft and shaft attachment have an axial stop 11 and 21. As arule, the two axial stops have surfaces which are produced with highprecision and are parallel to one another, whereby they contributesubstantially to the concentric running of shaft attachment and shaft.Further parts, for example a sealing or damping disk 3 as shown in thefigure, may be arranged between the axial stops.

[0025]FIG. 2 shows a section along the shaft axis through the connectionaccording to the invention. When the shaft attachment is screwed ontothe shaft, the two axial stops 11 and 21 are pressed together, as aresult of which the shaft attachment is prestressed against the shaft.

[0026] Since the shaft attachment, as a rule, is a larger part producedfrom a relatively soft material, the expansion of the shaft attachmentby the threaded stem can be prevented in the region of the threadedconnection by a hard steel sleeve 4 being pushed onto the shaftattachment.

[0027] The special design of the thread according to the invention isshown enlarged in FIG. 3. The thread has load-bearing flanks 15 and 25and production-related non-loaded flanks 16 and 26. The load-bearingflanks 15 and 25 enclose a very small angle αwith the axis A of theshaft and the shaft attachment. The flank angle α is ideally 5° to 15°,but, depending on the demands made on the connection or the material ofthe parts to be connected, may also be within the range of 0° to 45° oreven 60°. The smaller this angle α, the lower is the axial prestressingforce which can be transmitted by the thread in order to brace the twoparts to be connected, the shaft and the shaft attachment, against oneanother by means of the axial stops.

[0028] On the other hand, the radial pressure, decisive for the torquetransmission, in the case of a small angle between the load-bearingflanks and the axis is correspondingly larger. The load-bearing flanksbear frictionally on one another with their large surfaces.

[0029] For further reduction of the prestressing force, the threadaccording to the invention is of multiple-start, preferably 3-start,design. At a given flank angle, this results in thread grooves which areless deep and thus in less cross-sectional weakening. In addition, a3-start thread, on account of the triple cyclic symmetry, leads toimproved centering of the shaft attachment on the shaft.

[0030] Furthermore, the screw-on angle is greatly reduced by the largerhelix angle of the turns of the multiple-start thread.

[0031] The load-bearing flanks of flat design bring about a furtherimprovement in the centering of the shaft attachment on the shaft.

[0032] Compared with conventional threads, the flat thread according tothe invention has substantially larger fillet radii 17 and 27. As aresult, the thread according to the invention has virtually no notcheffect and can be loaded to a substantially greater extent with regardto dynamic torque fluctuations than a conventional thread.

[0033] If the thread is a conical thread, as shown in the variousfigures, the introduction of force is improved compared with acylindrical design, whereas the screw-on distances become shorter. Thesteeper the angle β of the cone, the shorter are the screw-on distances,since several thread turns can occasionally be skipped during thescrewing-on.

[0034] FIGS. 4 to 7 show detailed individual views of the shaft and theshaft attachment. The views in the axial direction show the three-startthreads. The three thread turns are each arranged offset by 120°.

[0035] The arrangement of the threaded stem and of the bore, or of theexternal and internal threads, may also be transposed, so that athreaded stem is arranged on the shaft attachment and the correspondingbore is incorporated in the shaft end.

[0036] Furthermore, the threaded stem need not be designed as a stub.Thus, for instance, the external thread may be arranged in a centerregion of a bar-shaped shaft, the bore in the shaft attachment having tobe correspondingly deep or continuous for the threaded extension.

LIST OF DESIGNATIONS

[0037] A Axis

[0038] α Flank angle

[0039] β Cone angle of the thread

[0040]1 Shaft, turbine shaft

[0041]10 Threaded stem

[0042]11 Shaft shoulder

[0043]15 Load-bearing flank (external thread)

[0044]16 Non-load-bearing flank (external thread)

[0045]17 Fillet (external thread)

[0046]2 Shaft attachment, compressor wheel

[0047]20 Threaded bore

[0048]21 Flat stop

[0049]25 Load-bearing flank (internal thread)

[0050]26 Non-load-bearing flank (internal thread)

[0051]27 Fillet (internal thread)

[0052]3 Intermediate body, seal

[0053]4 Steel sleeve

1. A connection of a shaft to a shaft attachment by means of a thread, abore with an internal thread being incorporated either in the shaftattachment or in the shaft end, and the shaft or the shaft attachmenthaving a corresponding stem which can be introduced into the threadedbore and has an external thread, and an axial stop being arranged ineach case on the shaft and on the shaft attachment, wherein the internaland external threads have torque-transmitting flanks which are flattoward the axis of shaft and shaft attachment and which can be connectedto one another frictionally by means of radial pressure by mutualrotation of shaft and shaft attachment with interaction between theaxial stops.
 2. The connection as claimed in claim 1, wherein thethreaded stem and the threaded bore are designed to be at least partlyconical, and wherein the thread is a conical thread.
 3. The connectionas claimed in claim 1, wherein the thread is a multiple-start, inparticular a three-start, thread.
 4. The connection as claimed in claim1, wherein the torque-transmitting flanks form an angle of less than45°, in particular between 5° and 15°, with the axis of shaft and shaftattachment.
 5. A turbocharger, comprising a turbine wheel and acompressor wheel connected to the turbine wheel via a shaft, the shaftand the compressor wheel being connected by means of a thread, a borewith an internal thread being incorporated either in the compressorwheel or in the shaft end, and the shaft or the compressor wheel havinga corresponding stem which can be introduced into the threaded bore andhas an external thread, and an axial stop being arranged in each case onthe shaft and on the compressor wheel, wherein the internal and externalthreads have torque-transmitting flanks which are flat toward the axisof shaft and shaft attachment and which can be connected to one anotherfrictionally by means of radial pressure by mutual rotation of shaft andshaft attachment with interaction between the axial stops.
 6. Theturbocharger as claimed in claim 5, wherein the threaded stem and thethreaded bore are designed to be at least partly conical, and whereinthe thread is a conical thread.
 7. The turbocharger as claimed in claim5, wherein the thread is a multiple-start, in particular a three-start,thread.
 8. The turbocharger as claimed in claim 5, wherein thetorque-transmitting flanks form an angle of less than 45°, in particularbetween 5° and 15°, with the axis of shaft and shaft attachment.